To enable a uniform output light ray having the desired color to be formed easily and economically by varying color and/or tone continuously through the movement relative to a light source of a plurality of filters which can block light rays from the light source.

A light source 13 connected to a transformer 14 covered with a casing 15 and an optical filter assembly 16 are enclosed in a casing 2, and a light ray F1 from the light source 13 is radiated parallel to an optical axis A. The optical filter 33 has surfaces 34 blocking the light ray F1 and consists of square elements which show subtractive primaries, cyan, yellow, and magenta, and which are slidable within a horizontal plane. The optical filter 33 is moved toward the front and rear of the figure by operating the operating rod of a moving assembly, to make the color and/or tone of the light ray F1 continuously variable. Thus the light ray F1 can be changed easily and economically into a uniform output light ray F2 with the desired color and/or tone.